Low Cost and High Performance Flip Chip Package

ABSTRACT

A low cost and high performance flip chip package is disclosed. By assembling the package using a substrate panel level process, a separate fabrication of a substrate is avoided, thus enabling the use of a coreless substrate. The coreless substrate may include multiple stacked layers of laminate dielectric films having conductive traces and vias. As a result, electrical connection routes may be provided directly from die contact pads to package contact pads without the use of conventional solder bumps, thus accommodating very high density semiconductor dies with small feature sizes. The disclosed flip chip package provides lower cost, higher electrical performance, and improved thermal dissipation compared to conventional fabricated substrates with solder bumped semiconductor dies.

BACKGROUND

To interface bare semiconductor dies to a support surface such as a printed circuit board, there is a need for an appropriate package substrate to interface and route the semiconductor dies within a package, such as a ball grid array (BGA) package, chip scale package (CSP), or system-in-package (SiP), to the printed circuit board. A conventional interface substrate may start with a core material with laminate film layers built up on both sides of the core material. A flip-chip die may then be coupled to the interface substrate using solder bumps.

Demand for higher performance, power efficiency, and reduced form factor have driven successive generations of die shrinks, resulting in flip-chip dies with very high density interconnect features. As the solder bump interconnects are also required to become increasingly dense, the manufacturability, cost, and reliability requirements for interface substrates have gradually become more difficult to meet. Moreover, with shrinking die sizes, effective thermal dissipation from the smaller available die surface area has also become a greater concern.

SUMMARY

The present disclosure is directed to low cost and high performance flip chip packages, substantially as shown in and/or described in connection with at least one of the figures, and as set forth more completely in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents a cross-sectional view of an exemplary flip-chip package using a conventional interface substrate.

FIGS. 2A, 2B, 2C, 2D, 2E, 2F and 2G present cross-sectional views of an exemplary flip chip package assembly.

DETAILED DESCRIPTION

The following description contains specific information pertaining to implementations in the present disclosure. One skilled in the art will recognize that the present disclosure may be implemented in a manner different from that specifically discussed herein. The drawings in the present application and their accompanying detailed description are directed to merely exemplary implementations. Unless noted otherwise, like or corresponding elements among the figures may be indicated by like or corresponding reference numerals. Moreover, the drawings and illustrations in the present application are generally not to scale, and are not intended to correspond to actual relative dimensions.

FIG. 1 presents a cross-sectional view of an exemplary flip-chip package using a conventional interface substrate. FIG. 1 includes package 100 (or “semiconductor package” 100), which includes flip chip 110 mounted on substrate 120 through a plurality of solder bumps, with an exemplary solder bump 115 as shown. Underfill 116 is also placed below flip chip 110 to support and insulate the plurality of solder humps 115. Substrate 120 includes a central core 140 having a plurality of vias, with an exemplary via 145 as shown. Central core 140 may have a thickness of 800 microns or more. An upper thin film 130 and a passivation layer 138 are formed above central core 140. Similarly, a lower thin film 150 and a passivation layer 158 are formed below central core 140. A plurality of conductive traces, with an exemplary conductive trace 122 as shown, is also formed within substrate 120 to route connections between the solder bumps of flip chip 110 and the solder balls of package 100, with an exemplary solder ball 105 as shown. Lid 160 may be adhesively attached to a backside of flip chip 110 and the top of substrate 120 to encapsulate package 100, as shown. Thus, package 100 is ready to be mounted to a support surface, such as a printed circuit board.

As discussed in the background, demand for higher performance, power efficiency, and reduced form factor have driven successive generations of die shrinks for flip chip 110, requiring a correspondingly higher pitch between solder bumps 115. For example, for a flip chip 110 using a 40 nm process, in high volume manufacturing, a 150 micron pitch is standard between solder bumps 115. However, solder bumping is quickly reaching its technological limit as the minimum practical solder bump pitch is considered to be 130 to 150 microns.

Flip chip 110 is manufactured using smaller feature sizes, such as 28 nm and below, solder bumping technology is unable to keep pace with the reduced bump pitch demanded of flip chip 110. Thus, a die size of flip chip 110 must increase, resulting in significant cost and form factor increases. Even if the die size of flip chip 110 is successfully reduced, effective thermal dissipation from the smaller die surface area also becomes a greater concern. Moreover, at fine solder bump pitch densities, reliability issues with the solder bump interconnects become increasingly pronounced, with solder joint cracking, electromigration performance degradation, and other issues resulting in lower yields and increased costs.

FIGS. 2A-2G present cross-sectional views of an exemplary flip chip package assembly. Starting with FIG. 2A, FIG. 2A includes panel substrate 270 with heat spreader 280 and backside tape 284. Heat spreader 280 may include electrically conductive materials such as copper or other metals. Backside tape 284 may be applied to heat spreader 280 for mechanical protection and support during assembly, as known in the art. A plurality of recesses in heat spreader 280, with exemplary recess 282 as shown, are provided for receiving dies. While only three recesses are shown in the cross-sectional view of FIG. 2A, it should be understood that panel substrate 270 may accommodate recess grids of any size.

Next, in FIG. 2B, an adhesive thermal interface material (TIM) 286 is printed through mask 285 and into recesses 282 of heat spreader 280. Although adhesive TIM 286 is utilized in FIG. 2B, any die attach material or method of attachment may also be utilized.

Continuing with FIG. 2C, a semiconductor die may be placed in each of recesses 286 of heat spreader 280, with exemplary semiconductor die 210 as shown. Each semiconductor die 210 includes a plurality of die contact pads, with exemplary die contact pad 212 as shown. Die contact pads 212 may be electrically conductive materials such as copper or other metals. Each semiconductor die 210 may be a flip-chip. After situating the semiconductor dies 210 in respective recesses 286, adhesive TIM 286 may spread to attach each of the semiconductor dies 210 to heat spreader 280, as shown.

Moving to FIG. 2D, laminate dielectric film 230 a may be formed over semiconductor dies 210 and heat spreader 280. Laminate dielectric film 230 a may utilize organic materials such as Bismaleimide-Triazine (BT), Ajinomoto Build-up Film (ABF), FR-4 laminates, E679-FBG, ECL4785GS, and E700.

Turning to FIG. 2E, a first level interconnect is created. First, a plurality of vias, with an exemplary via 232 as shown, is formed through laminate dielectric film 230 a, for example by laser drilling. Next, the plurality of vias 232 and the top of laminate dielectric film 230 a are plated to form a plurality of traces, with an exemplary trace 234 as shown. The plated plurality of vias 232 and the plurality of traces 234 may be electrically conductive materials such as copper or other metals, and may also be the same materials as the plurality of die contact pads 212. As a result, the plurality of vias 232 may be directly connected to a respective plurality of die contact pads 212. Thus, the plurality of semiconductor dies 210 may have no flip chip solder bumps for each respective die contact pad 212. The plurality of vias 232 may eventually connect to a respective plurality of package contact pads, as discussed below.

In FIG. 2F, an additional two levels of interconnects are created. However, any number of interconnect levels may be provided by repeating, for as many levels as necessary, the formation of laminate dielectric films, vias, and traces as demonstrated in FIGS. 2D and 2E. As shown in FIG. 2F, laminate dielectric film 230 b and laminate dielectric film 230 c are formed to create a stack of laminate dielectric films 290. Laminate dielectric films 230 a, 230 b, and 230 c may all utilize the same materials, such as ABF. A plurality of package contact pads 202, with an exemplary package contact pad 202 as shown, is formed above the stack of laminate dielectric films 290. The plurality of package contact pads 202 may be electrically conductive materials such as copper or other metals, and may be surrounded by a solder resist 204, as shown. The traces and vias within the stack of laminate dielectric films 290 combine to form a plurality of electrical connection routes 295, connecting the plurality of die contact pads 212 to a respective plurality of package contact pads 202. As a result, the plurality of vias 232 in the lower laminate dielectric film 230 a is also electrically connected to a respective plurality of package contact pads 202.

Subsequently, in FIG. 2G, panel substrate 270 undergoes singulation to result in packages 200 a, 200 b, and 200 c. The backside tape 284 is also removed after singulating. Thus, a flip chip package is provided where the package substrate 206 tightly integrates the semiconductor die 210 without the use of solder bump interconnects. Solder balls may be coupled to package contact pads 202 to prepare packages 200 a, 200 b, and 200 c for flipping onto a support surface such as a printed circuit board. Flip chip package 200 a in FIG. 2G provide several advantages compared to the conventional flip chip package 100 in FIG. 1. First, since the process of assembling package 200 a does not utilize flip chip solder bumps, such as solder bumps 115, the associated processes of solder bumping, reflowing, defluxing, and adding underfill 116 may be advantageously avoided. Since the pitch between die contact pads 212 is no longer limited by solder bump technology, very high density semiconductor dies 210 may be supported, as the new technological limitation is the alignment of vias 232 to corresponding die contact pads 212. With present laser via drilling processes, a minimum supported pitch between die contact pads 212 can be as low as 15 microns for high volume manufacturing and approximately 12.5 microns for low volume manufacturing, compared to the limit of 130 to 150 microns for solder bumping.

Since reflow processes can be avoided entirely and the formation of vias 232 can be carried out at essentially room temperature, coefficient of thermal expansion (CTE) mismatches arising from such reflow processes are also advantageously avoided. Conductivity and electromigration performance is also improved as electrical connection routes 295 may be composed wholly of highly conductive materials such as copper, in comparison to the required solder bumps 115 of package 100.

Furthermore, the tight coupling of semiconductor die 210 to package substrate 206 eliminates the need for a separate substrate fabrication process as package 200 a is assembled using a substrate panel level process. Thus, central core 140 of substrate 120 may be completely omitted in package substrate 206, resulting in a coreless substrate. Thus, pre-soldering, core materials, and core via drilling and plating steps may be omitted, and layer counts may also be reduced as layers do not need to be built on both sides of a core. By reducing the number of required steps and materials, a very cost effective package assembly may be provided while providing a thinner form factor and higher electrical performance. Moreover, since heat spreader 280 is already an integral part of package 200 a and is coupled to semiconductor die 210 via a surrounding adhesive TIM 286, improved thermal dissipation may be provided and package height may be even further reduced as a separate heat sink is not required.

With regards to electrical performance, according to electrical simulations, package 200 a may be expected to have an approximately 60% reduction in package resistance and an approximately 70% reduction in inductance when compared to package 100, both considerable improvements. However, since capacitance is largely related to the build-up stack of laminate dielectric films 290, little variance in capacitance is expected between package 100 and package 200 a. The removal of the thick central core 140 with its large vias 145 is also expected to provide significant improvements in crosstalk, simultaneous switching output (SSO) noise, and signal path impedance mismatch, which in turn reduces serial interface differential return loss and parallel interface signal reflection. These signal improvements may be especially relevant for high speed, high density memory devices.

From the above description it is manifest that various techniques can be used for implementing the concepts described in the present application without departing from the scope of those concepts. Moreover, while the concepts have been described with specific reference to certain implementations, a person of ordinary skill in the art would recognize that changes can be made in form and detail without departing from the spirit and the scope of those concepts. As such, the described implementations are to be considered in all respects as illustrative and not restrictive. It should also be understood that the present application is not limited to the particular implementations described herein, but many rearrangements, modifications, and substitutions are possible without departing from the scope of the present disclosure. 

1. A semiconductor package comprising: a heat spreader having a recess; a semiconductor die situated in said recess and attached to said heat spreader, said semiconductor die having a plurality of die contact pads; a package substrate comprising at least one laminate dielectric film; a plurality of vias within said at least one laminate dielectric film for connecting said plurality of die contact pads to a corresponding plurality of package contact pads.
 2. The semiconductor package of claim 1, wherein said semiconductor die is a flip chip including said plurality of die contact pads and having no flip chip solder bumps.
 3. The semiconductor package of claim 2 wherein said plurality of vias are directly connected to said plurality of die contact pads.
 4. The semiconductor package of claim 1, wherein said package substrate is coreless.
 5. The semiconductor package of claim 1, wherein said semiconductor die is attached to said heat spreader by adhesive thermal interface material (TIM).
 6. The semiconductor package of claim 1, wherein said at least one laminate dielectric film is an Ajinomoto Build-up Film (ABF).
 7. A semiconductor package comprising: a heat spreader having a recess; a semiconductor die situated in said recess and attached to said heat spreader, said semiconductor die having a plurality of die contact pads; a package substrate comprising a stack of laminate dielectric films; a plurality of electrical connection routes within said stack of laminate dielectric films for connecting said plurality of die contact pads to a corresponding plurality of package contact pads.
 8. The semiconductor package of claim 7, wherein said semiconductor die is a flip chip including said plurality of die contact pads and having no flip chip solder bumps.
 9. The semiconductor package of claim 8, wherein a plurality of vias in a lower laminate dielectric film in said stack of laminate dielectric films are directly connected to said plurality of die contact pads.
 10. The semiconductor package of claim 8, wherein said package substrate is coreless.
 11. The semiconductor package of claim 8, wherein said semiconductor die is attached to said heat spreader by adhesive thermal interface material (TIM). 12-20. (canceled) 